T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer of immature T lymphoblasts for which current therapies are highly toxic and ineffective in many patients. The precedent of imatinab in Chronic myelogenous leukemia (CML) demonstrates the great potential of drugs that target molecular lesions specific to cancer cells. T-ALL patients frequently have genetic alterations that activate the Ras/PI3K/Akt pathway and Notch1, thus testing inhibitors of these pathways is a high priority. In addition, greater understanding of the molecular and biochemical basis of T lineage leukemic growth will likely reveal novel drug targets. Retroviral insertional mutagenesis (RIM) is a powerful strategy for introducing genetic alterations that can be traced and identified. I previously used RIM to find genes that cooperate with oncogenic K-Ras (KrasG12D) to induce acute leukemia. Infecting KrasG12D mice with the MOL4070 retrovirus resulted in a high incidence of T-ALL that frequently harbored somatic Notch1 mutations as well as diverse genetic lesions generated by RIM. Using this strategy, I have generated a cohort of 70 primary transplantable T-ALLs that display remarkable biochemical and genetic heterogeneity thereby recapitulating the diversity observed in human cancer. The overall goals of this K99/R00 proposal are to test treatment strategies that target T-ALL molecular lesions in vivo, analyze acquired drug resistance, and uncover genes and biochemical pathways that underlie T cell transformation two specific aims: 1) To investigate the effects of a small molecule inhibitor of PI3K alone or in combination with other therapeutic agents on leukemic growth in vivo and to identify genes that modulate drug sensitivity and resistance; 2) To identify mechanisms of Notch1-independent growth in T-ALL. This K99/R00 award will provide me with the resources, time and training necessary to apply the T-ALL model I have developed to important preclinical and mechanistic questions. It will allow me to transition into the field of translational cancer research and generate data and reagents that will be the foundation for my own independent research laboratory. This award will enable me to achieve the following career goals: 1) Develop knowledge and experience in preclinical trial design and application; 2) Learn techniques to manipulate primary murine cells; and 3) Gain experience working with human patient samples. During the mentored phase I will conduct several preclinical trials, determine biomarkers of therapeutic response, investigate resistance mechanisms to a PI3 Kinase inhibitor, and identify genes/signaling pathways deregulated in T-ALLs that lack active Notch1. During the independent phase I will evaluate and validate resistance to drug combinations, validate molecules/pathways that substitute for active Notch1, and test therapies directed at novel drug resistance and leukemogenesis pathways I identify in Aims 1 and 2. Overall these studies will test novel therapeutic strategies and identify new drug targets leading to improved treatment options for T-ALL patients.